Hydraulic drive vehicle

ABSTRACT

A hydraulic driving vehicle comprises front and rear transaxles incorporating respective hydraulic motors, and a pump unit separated from the front and rear transaxles. The pump unit incorporates a hydraulic pump having a pump shaft. A hydraulic circuit is formed by piping between the pump unit and the front and rear transaxles so as to circulate hydraulic fluid between the hydraulic pump and the hydraulic motors. A reservoir tank of the hydraulic fluid is connected to the hydraulic circuit by piping. A first cooling fan blowing air away from the pump unit and a second cooling fan blowing air toward the pump unit are disposed oppositely to each other with respect to the pump unit and drivingly connected to the pump shaft. At least a pipe for the piping of the hydraulic circuit and the reservoir tank passes an area blown by each of the first and second cooling fans.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a hydraulic driving vehicle comprising a pairof front and rear transaxles incorporating respective hydraulic motors,supplied with hydraulic fluid through pipes from a pump unit separatedfrom the transaxles.

2. Related Art

Conventionally, there is a well-known working vehicle having front andrear transaxles incorporating respective hydraulic motors, which aresupplied with hydraulic fluid from a pump unit separated from thetransaxles, as disclosed in U.S. Pat. No. 6,732,828. Pipes areinterposed among the pump unit and the front and rear transaxles so asto form a hydraulic circuit for circulating hydraulic fluid between ahydraulic pump in the pump unit and the hydraulic motors in thetransaxles.

Hydraulic fluid circulated in the hydraulic circuit is heated as much asits pressure loss. Therefore, a cooling fan is usually provided on apump shaft of the hydraulic pump projecting outward from a casing of thepump unit so as to blow and cool the casing, thereby cooling thecirculated hydraulic fluid.

However, the effect of cooling hydraulic fluid is insufficient becausethe cooling effect by the cooling fan is transmitted to the hydraulicfluid through the casing of the pump unit.

Further, conventionally, a reservoir tank is fluidly connected through apiping to the hydraulic circuit including the hydraulic pump and motorsso as to absorb excessive hydraulic fluid. The problem of the reservoirtank is that the absorption of excessive fluid from any of the pump unitand transaxles interferes with flow of fluid through another of the pumpunit and transaxles.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a hydraulicdriving vehicle comprising front and rear transaxles incorporatingrespective hydraulic motors and a pump unit separated from the front andrear transaxles which are fluidly connected by piping so as to form ahydraulic circuit for circulating hydraulic fluid among a hydraulic pumpin the pump unit and the hydraulic motors in the transaxles, a reservoirtank being fluidly connected to the hydraulic circuit by piping, whereinthe effect of cooling the hydraulic fluid circulated in the hydrauliccircuit is enhanced.

To achieve the first object, according to the present invention, thehydraulic driving vehicle comprises a first cooling fan drivinglyconnected to the pump shaft so as to blow air away from the pump unit,wherein at least one pipe for the piping of the hydraulic circuit andthe reservoir tank passes an area blown by the first cooling fan so asto effectively cool the hydraulic fluid circulating in the hydrauliccircuit.

Preferably, one of the front and rear transaxles is disposed within anarea blown by air from the first cooling fan so as to enhance the effectof cooling the transaxle and hydraulic fluid in the hydraulic circuit.

Preferably, the hydraulic driving vehicle further comprises a secondcooling fan drivingly connected to the pump shaft opposite to the firstcooling fan with respect to the hydraulic pump, wherein the secondcooling fan blows air toward the pump unit, and at least one pipe forthe piping of the hydraulic circuit and the reservoir tank passes anarea blown by the second cooling fan so as to enhance the effect ofcooling the hydraulic fluid circulating in the hydraulic circuit.

Preferably, at least one pipe for the piping of the hydraulic circuitand the reservoir tank is partly or entirely made of metal material soas to be cooled effectively.

Preferably, the vehicle further comprises a hydraulic actuator and apipe for piping the hydraulic actuator to the hydraulic circuit passesthe area blown by the first or second cooling fan so as to effectivelycool hydraulic fluid supplied to the hydraulic actuator.

A second object of the present invention is to provide a hydraulicdriving vehicle comprising front and rear transaxles incorporatingrespective hydraulic motors to which a hydraulic pump separated from thefront and rear transaxles is fluidly connected by piping so as to form ahydraulic circuit for circulating hydraulic fluid among the hydraulicpump and motors, wherein a reservoir tank is fluidly connected to thehydraulic circuit without excessive hydraulic fluid of any of the pumpunit and transaxles in the hydraulic circuit interfering with hydraulicfluid flow of any of the hydraulic pump and motors.

To achieve the second object, according to the present invention, thefront and rear transaxles and the pump unit are connected throughrespective separate pipes to the reservoir tank so as to returnexcessive fluid to the reservoir tank, whereby each of the hydraulicpump and motors is free of action from influence of fluid flow from anyof the pump unit and transaxles to the reservoir tank.

These, other and further objects, features and advantages will appearmore fully from the following description with reference to accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic right side view of a riding lawn mower vehicle 1serving as a hydraulic driving working vehicle according to anembodiment of the present invention.

FIG. 2 is a schematic plan view of vehicle 1 showing a hydraulic circuitsystem with piping for driving vehicle 1 (the shown piping is sorearranged for convenience as to be different from its actual planview).

FIG. 3 is a diagram of the hydraulic circuit system.

FIG. 4 is a sectional right side view of a portion of vehicle 1, showinga pump unit 30, a rear transaxle 10B and a reservoir tank 40 connectedto each other by piping.

FIG. 5 is a sectional rear view of the same portion of vehicle 1 shownin FIG. 4.

FIG. 6 is an enlarged rear view partly in section of the same portion ofvehicle 1 shown in FIG. 4, showing pump unit 30 and reservoir tank 40.

FIG. 7 is a fragmentary enlarged sectional rear view of the same portionof vehicle 1 shown in FIG. 4, showing a neutral returning mechanism of ahydraulic motor 33 in pump unit 30. FIG. 7( a) is a sectional view of aneutral adjusting sleeve 42 and a shaft 41 therein.

FIG. 8 is an enlarged sectional side view of pump unit 30 showing adraining valve 50.

FIG. 9 is a bottom view of transaxle 10A (may be replaced with transaxle10B) with a bottom casing part 61A removed.

FIG. 10 is a sectional right side view of transaxle 10A (or 10B) showinga hydraulic motor 11A (may be replaced with a hydraulic motor 11B) and adifferential locking mechanism therein.

FIG. 11 is a sectional left side view of transaxle 10A (or 10B) showinga deceleration gearing therein.

FIG. 12 is a sectional rear view of transaxle 10A (or 10B) showing adifferential gearing therein.

FIG. 13 is a sectional front view of transaxle 10A (or 10B) showinghydraulic motor 11A (or 11B) therein in a case where a clutch is notinterposed between a motor shaft 11 a and a motor gear 11 d.

FIG. 14 is a sectional front view of transaxle 10A (or 10B) showinghydraulic motor 11A (or 11B) therein in a case where a clutch device 96is interposed between motor shaft 11 a and a motor gear 11 m.

FIG. 15 is a fragmentary enlarged front view partly in section oftransaxle 10A (or 10B) showing a mechanism including a shaft holder 15holding a control shaft 14 for defining a tilt angle range of a movableswash plate 11 c. FIG. 15( a) is a sectional front view (a) of shaftholder 15.

FIG. 16 is a similar view of transaxle 10A (or 10B) showing the abovemechanism having shaft holder 15 arranged corresponding to movable swashplate 11 c whose rotational direction relative to hydraulic fluid flowdirection is opposite to that of FIG. 15.

FIG. 17 is a similar view of transaxle 10A (or 10B) showing the abovemechanism having shaft holder 15 arranged for fixing swash plate 11 c soas to fix the displacement of corresponding hydraulic motor 11A (or11B).

FIG. 18 is an enlarged sectional side view of a portion of vehicle 1including a mechanism of supporting transaxle 10A to a chassis 3.

FIG. 19 is an enlarged sectional rear view of the portion of vehicle 1shown in FIG. 18.

FIG. 20 is an enlarged plan view of the portion of vehicle 1 shown inFIG. 18.

FIG. 21 is a fragmentary enlarged sectional front view of the portion ofvehicle 1 shown in FIG. 18 showing a linkage between a right tire 140Rand a control lever 23 for controlling swash plate 11 c with a guidemechanism 150.

FIG. 22 is a schematic side view of an articulate working vehicle 200according to the present invention.

FIG. 23 is a schematic plan view of vehicle 200 showing a hydrauliccircuit system with piping for driving vehicle 200 (the shown piping isso rearranged for convenience as to be different from its actual planview).

FIG. 24 is a table showing two motor setting patterns of transaxles 10Aand 10B.

FIG. 25 is a side view of a principal portion of vehicle 1 or 200showing alternatively arranged pump unit 30.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of a hydraulic driving working vehicle according to thepresent invention will be described.

Referring to a working vehicle 1 shown in FIGS. 1 and 2, a fronttransaxle 10A, a rear transaxle 10B, and a mower 2 between transaxles10A and 10B are disposed below a chassis 3. Rear transaxle 10B islaterally eccentrically disposed in vehicle 1 so that left and rightaxles 19L and 19R projecting laterally outward from rear transaxle 10Bare different in length from each other. Left and right brackets 3 aholding respective bearings are hung down from chassis 3 so as tojournal respective axles 19L and 19R through the respective bearingsadjacent to rear tires on outer ends of axles 19L and 19R. Fronttransaxle 10A is suspended from chassis 3 as discussed later. An engine4, and a pump unit 30 incorporating a hydraulic pump 33 driven by engine4 are mounted on chassis 3. Engine 4 and pump unit 30 are enclosed in abonnet 5 on which a driver's seat 6 is mounted.

A steering wheel 7 is disposed in front of seat 6, and aspeed-controlling pedal 8 is disposed below steering wheel 7.Speed-controlling pedal 8 is operatively connected to a speed controllever 31 a of pump unit 30 via a linkage 9 so as to change the variabledisplacement of hydraulic pump 33 in pump unit 30, thereby changing thetraveling speed of working vehicle 1.

Referring to FIG. 2, pump unit 30 and a reservoir tank 40 are disposedbetween front and rear transaxles 10A and 10B. Referring to FIGS. 2 and3, pump unit 30 incorporates variable displacement hydraulic pump 33shown in FIG. 3. Front transaxle 10A incorporates a front hydraulicmotor 11A, and rear transaxle 10B a rear hydraulic motor 11B.

Alternatively, pump unit 30 may be disposed before front transaxle 10Aor behind rear transaxle 10B. Alternatively, pump unit 30 may bedisposed over or below the longer one of axles 19L and 19R of reartransaxle 10B disposed laterally eccentrically as mentioned above sothat pump unit 30 and rear transaxle 10B are laterally juxtaposedbetween left and right brackets 3 a. Pump unit 30 may be disposed at anyplace in vehicle 1 if the place is appropriate for avoiding interferencewith another part or member and for ensuring its proper drivingconnection with engine 4.

By piping among transaxles 10A and 10B and pump unit 30, a hydrauliccircuit among hydraulic pump 33 and motors 11A and 11B is formed so asto connect hydraulic motors 11A and 11B in tandem to pump 33. Whenvehicle 1 travels forward, hydraulic fluid delivered from pump 33 flowsthrough one of motors 11A and 11B, then flows through the other motor11B or 11A, and returns to pump 33. In this way, the hydraulic fluid iscirculated in the hydraulic circuit. When vehicle 1 travels backward,the hydraulic fluid flows in the hydraulic circuit in the oppositedirection.

Pump unit 30 incorporates a charge pump 32 shown in FIG. 3 so as tocharge hydraulic fluid from reservoir tank 40 into a higher pressuredhydraulic fluid delivery passage in the hydraulic circuit.

Transaxles 10A and 10B have respective hydraulic fluid sumps therein,and have respective drain ports 10 a and 10 b open to the fluid sumps. Apipe 81 is interposed between drain port 10 a of transaxle 10A andreservoir tank 40, and a pipe 82 between drain port 10 b of transaxle10B and reservoir tank 40, thereby draining excessive hydraulic fluidfrom respective transaxles 10A and 10B to reservoir tank 40.

In FIG. 1 illustrating entire vehicle 1, the piping among transaxles 10Aand 10B and pump unit 30 for forming the HST circuit and to reservoirtank 40 is omitted.

Pump unit 30 has a drain port 30 q shown in FIG. 3. A pipe 87 isinterposed between drain port 30 q and reservoir tank 40 so as to drainexcessive hydraulic fluid from pump unit 30 to reservoir tank 40.

Pump unit 30 has a pair of PTO ports 30 r and 30 s, as shown in FIG. 3.A hydraulic actuator 100 such as a hydraulic cylinder for power steeringor power lifting is optionally fluidly connected to the hydrauliccircuit via pipes 88 and 89 coupled to respective PTO ports 30 r and 30s.

A breather 40 d is disposed on the top of reservoir tank 40 so as torelease air from reservoir tank 40 to the atmosphere.

In this way, transaxles 10A and 10B and pump unit 30 are fluidlyconnected to reservoir tank 40 via respective separate pipes 81, 82 and87, so that excessive hydraulic fluids from transaxles 10A and 10B andpump unit 30 directly flow into reservoir tank 40 independently of oneanother.

If the excessive hydraulic fluids from transaxles 10A and 10B and pumpunit 30 were collected before flowing into reservoir tank 40, theresistance of the hydraulic fluid to flowing would increased so as todestabilize the flow of hydraulic fluid among transaxles 10A and 10B andpump unit 30, i.e., to hinder exact operations of hydraulic pump 33 andmotors 11A and 11B. The above piping of separate pipes 81, 82 and 87 toreservoir tank 40 from respective transaxles 10A and 10B and pump unit30 prevents hydraulic pump 33 and motors 11A and 11B from interferingwith one another in operation, thereby ensuring exact operations ofthem.

Referring to FIG. 5, pipes 81, 82, 86 and 87 are extended or bent upwardto connect at tops thereof to the bottom end of reservoir tank 40.Therefore, the top open ends of pipes 81, 82, 86 and 87 are constantlydisposed below the level of hydraulic fluid in reservoir tank 40 so asto prevent the drained fluid from hitting the fluid level surface in thereservoir tank 40 causing air bubble in the fluid in the hydrauliccircuit.

Referring to hydraulic fluid pipes shown in FIGS. 2 to 6, pipes 81 and82 serve as drain passages from the respective hydraulic motor chambersof transaxles 10A and 10B to reservoir tank 40, as mentioned above. Apipe 83 is interposed between pump unit 30 and rear transaxle 10B. Apipe 84 is interposed between front and rear transaxles 10A and 10B. Apipe 85 is interposed between front transaxle 10A and pump unit 30. Eachof pipes 81, 84 and 85 includes a rubber tube portion which is flexibleand proof against high pressure of the hydraulic fluid.

Pipes 86 and 87 are interposed between pump unit 30 and reservoir tank40. Pipe 86 connects charge pump 32 in pump unit 30 to reservoir tank 40so as to charge a part of the hydraulic circuit in pump unit 30 withhydraulic fluid from reservoir tank 40. Pipe 87 is provided for draininghydraulic fluid from a fluid sump of pump unit 30 to reservoir tank 40.

Preferably, pipes 81 to 89 are partly or entirely made of metal materialhaving effective radiation of heat from hydraulic fluid therein.

Pump unit 30 uprightly mounted on chassis 3 will be described inaccordance with FIGS. 4 to 6 and others. Referring to FIG. 6, a lowercasing 30 a is fixedly mounted upright on chassis 3 to rotatably supporta vertical pump shaft 30 p of hydraulic pump 33. A middle casing 30 c,whose internal space serves as a pump chamber 30 b for incorporatinghydraulic pump 33, is fixedly mounted upright on lower casing 30 a. Acenter section 30 d formed therein with hydraulic fluid ducts is fixedlymounted upright on middle casing 30 c. Upper casing 30 e is fixedlymounted upright on center section 30 d. Charge pump 32 is formed inupper casing 30 e.

Variable displacement hydraulic pump 33 disposed in pump chamber 30 bcomprises a cylinder block 33 a and a movable swash plate 33 b.Speed-control lever 31 a is provided on an outer side of middle casing30 c so as to change the tilt angle of swash plate 33 b.

Vertical pump shaft 30 p of hydraulic pump 33 is disposed at the top endthereof in center section 30 d. A vertical pump shaft 34 a of chargepump 32 in upper casing 30 e just above center section 30 d is extendeddownward so that coaxial pump shafts 30 p and 34 a integrally rotatablyengage with each other in center section 30 d. The top portion of chargepump shaft 34 a projects upright from upper casing 30 e so as to befixedly provided thereon with a cooling fan 34 b. Due to thisconstruction, by rotating pump shaft 30 p, cooling fan 34 b rotates toblow air downward to pump unit 30 and pipes 83, 85, 86 and 87 connectedto pump unit 30, as shown in FIG. 5.

Referring to FIG. 6, the bottom portion of pump shaft 30 p projectsdownward from chassis 3 so as to be fixedly provided thereon with apulley 35 and a cooling fan 36. As shown in FIG. 1, a driving belt 4 cis interposed between pulley 35 and a pulley 4 b fixed on an outputshaft 4 a of engine 4 so as to rotate pump shaft 30 p by the power ofengine 4.

Cooling fan 36 blows air downward to rear transaxle 10B and pipes 82,83, 84 and 85 connected to rear transaxle 10B. Alternatively, coolingfan 36 may be provided on extended output shaft 4 a of engine 4 if theeffect of cooling all or a part of the pipes and rear transaxle 10B isensured.

To sum up, pipes 82, 83, 84 and 85 connected to rear transaxle 10B passan area blown by first cooling fan 36 drivingly connected to pump shaft30 p, and pipes 83, 85, 86 and 87 connected to pump unit 30 pass an areablown by second cooling fan 34 b drivingly connected to pump shaft 30 popposite to first cooling fan 36 with respect to hydraulic motor 33.First cooling fan 36 blows air away from pump unit 30, and secondcooling fan 34 b toward pump unit 30. Such an arrangement of the pipesrelative to opposite first and second cooling fans 36 and 34 beffectively cools hydraulic fluid in the pipes, i.e., hydraulic fluidcirculated among the hydraulic circuit of pump 33 and motors 11A and11B.

Incidentally, at least one of pipes 88 and 89 between pump unit 30 andhydraulic actuator 100, as shown in FIG. 3, may also pass the area blownby the first or second cooling fan 36 or 34 a so as to effectively coolhydraulic fluid supplied to hydraulic actuator 100.

The arrangement of the pipes as shown in FIG. 4 is an example.Alternatively, all pipes 81 to 87 (shown in FIG. 2) may pass the areablown by either cooling fan 34 b or 36.

Rear transaxle 10B is disposed in the area blown by cooling fan 36 onpump shaft 30 p of pump unit 30, thereby being effectively cooled, andfurther facilitating for cooling hydraulic fluid in the hydrauliccircuit. Alternatively, if pump unit 30 is disposed adjacent to fronttransaxle 10A, front transaxle 10A may be disposed in the area blown bycooling fan 36 (or 34 b).

Alternatively, pump unit 30 may be disposed to orient pump shaft 30 phorizontally, if it can be drivingly connected to engine 4 properly.

Referring to reservoir tank 40 as shown in FIG. 6, a stay 40 a is fixedat a lower portion thereof to middle casing 30 c, and has a tophorizontal plate portion 40 b on which reservoir tank 40 is mountedupright above cooling fan 34 b. The above-mentioned pipes 81, 82 and 86are connected upward to the bottom of reservoir tank 40 on top portion40 b of stay 40 a. Referring to FIG. 6, reservoir tank 40 is providedwith a filter 40 c from which pipe 86 is extended to charge pump 32 inpump unit 30. Alternatively, stay 40 a may be fixed to chassis 3 insteadof middle casing 30 c.

Illustrated reservoir tank 40 is integrated to pump unit 30 through stay40 a and disposed laterally adjacent to pump unit 30. Alternatively,reservoir tank 40 may be separated from pump unit 30. Any place invehicle 1 may be allowed for arranging reservoir tank 40 if reservoirtank 40 can be disposed well without interfering with another member orpart.

Further, the bottom of reservoir tank 40 to which top ends of pipes 81,82 and 86 is connected is disposed higher than charge pump 32 so as tofacilitate easy escape of air from the hydraulic fluid pipes intoreservoir tank 40. Alternatively, reservoir tank 40 may be disposed ashigh as or slightly lower than charge pump 32 if such a high placecannot be provided for reservoir tank 40 and the force of charge pump 32for circulating hydraulic fluid is sufficient to force air fromhydraulic fluid circulating in the HST circuit into reservoir tank 40.

Referring to FIGS. 4 to 6, a neutral returning mechanism 31 forreturning swash plate 3 b to its neutral position (for stopping thedelivery of hydraulic fluid by hydraulic pump 33) is disposed adjacentto control lever 31 a. Control lever 31 a has a branching second lever31 b from which a horizontal pin 31 c projects. A neutral adjustingshaft 37 is planted into a stay 37 a fixed onto an outer side end ofmiddle casing 30 c so as to project from stay 37 a in parallel to pin 31c. A portion 37 c of shaft 37 projecting from stay 37 a is eccentric tothe remaining portion 37 b of shaft 37 in stay 37 a. A nut is screwed ona threaded portion of shaft 37 projecting from stay 37 a opposite toportion 37 c so as to fasten shaft 37 to stay 37 a. By loosening thenut, portion 37 c is allowed to revolve around portion 37 b so as toadjust the neutral position of control lever 31 a in correspondence tothe neutral position of swash plate 33 b.

A horizontal speed-control shaft 39 b is rotatably supported by middlecasing 30 c and projects out from middle casing 30 c so as to be fixedlyprovided thereon with a cylinder 39 a. Speed-control lever 31 a is fixedat its basic portion onto cylinder 39 a. A neutral returning spring 38is coiled and retainer on cylinder 39 a. Both end portions 38 a and 38 bof spring 38 are twisted to cross each other and extended in parallel soas to nip pin 31 c and portion 37 c of shaft 37 at their initial(neutral) positions.

Speed-control shaft 39 b is fixed to one end of an arm 39 c in pumpchamber 30 b enclosed by middle casing 30 c. A fitting portion 39 dformed on the other end of arm 39 c is fitted to a fitting portion 33 fof swash plate 33 b.

Due to the above, depression of speed-control pedal 8 shown in FIG. 1rotates speed-control lever 31 a so as to rotate cylinder 39 a, shaft 39b and arm 39 c, thereby tilting swash plate 33 b to a target positionfor determining amount and direction of hydraulic fluid delivered fromhydraulic pump 33. Pin 31 c rotating together with levers 31 a and 31 bby depression of pedal 8 pushes one of end portions 38 a and 38 b ofspring 38 away from the other end portion 38 b or 38 a of spring 38retained by shaft 37, thereby being biased by spring 38 toward itsneutral position. By releasing pedal 8 from the depression force, endportion 38 a or 38 b abutting against pin 31 c returns to its initialposition so as to push pin 31 c toward shaft 37, thereby returning lever31 a and swash plate 33 b together to their neutral positions.

An alternative neutral returning mechanism 31′ is shown in FIGS. 7 and7( a), with a horizontal shaft 41 screwed at one end portion thereofinto center section 30 d, and extended out from center section 30 d soas to be inserted into a hole 42 a axially penetrating a neutraladjusting sleeve 42. Hole 42 a is eccentric to the central axis ofsleeve 42. A nut is screwed on the other end portion of shaft 41projecting out from sleeve 42 opposite to center section 30 d so as tofasten shaft 41 to center section 30 d. By loosening the nut, sleeve 42is allowed to revolve around shaft 41 so as to adjust the neutralposition of a speed-control lever 31 n operatively connected tospeed-control pedal 8 in correspondence to the neutral position of swashplate 33 b.

Horizontal speed-control shaft 39 b rotatably supported by middle casing30 c is fixed to arm 39 c in pump chamber 30 b enclosed by middle casing30 c so as to be fitted to swash plate 33 b, similarly to that of FIG.6. Speed-control shaft 39 b projects out from middle casing 30 c so asto be fixedly provided thereon with a cylinder 39 m. Speed-control lever31 n operatively connected to speed-control pedal 8 is fixed at itsbasic portion 31 p onto an outer end portion of speed-control shaft 39 bprojecting outward from cylinder 39 m. A lever 31 q is extended frombasic portion 31 p oppositely to speed-control lever 31 n. A horizontalpin 31 r projects from an utmost end of lever 31 q in parallel to sleeve42. A neutral returning spring 138 is coiled and retained on cylinder 39m. Both end portions 138 e and 138 f of spring 138 are twisted to crosseach other and extended in parallel so as to nip pin 31 r and sleeve 42at their initial (neutral) positions.

Due to the above, depression of speed-control pedal 8 shown in FIG. 1rotates speed-control lever 31 n so as to rotate cylinder 39 m, shaft 39b and arm 39 c, thereby tilting swash plate 33 b to a target positionfor determining amount and direction of hydraulic fluid delivered fromhydraulic pump 33. Pin 31 r rotating together with levers 31 n and 31 qby depression of pedal 8 pushes one of end portions 138 e and 138 f ofspring 138 away from the other end portion 138 f or 138 e of spring 138retained by sleeve 42, thereby being biased by spring 138 toward itsneutral position. By releasing pedal 8 from the depression force, endportion 138 e or 138 f abutting against pin 31 r returns to its initialposition so as to push pin 31 r toward sleeve 42, thereby returninglever 31 n and swash plate 33 b together to their neutral positions.

In comparison with neutral returning mechanism 31 of FIG. 6, alternativeneutral returning mechanism 31 is simple because shaft 41 planted intocenter section 30 d requires no stay like stay 37 a.

A bypass valve 50 as shown in FIG. 8 is interposed on a bypass duct 51between the higher and lower pressured hydraulic oil ducts in pump unit30, as shown in FIG. 3. Bypass valve 50 normally cuts off bypass duct 51so as to ensure the proper circulation of hydraulic fluid between thehigher and lower pressured hydraulic fluid ducts in pump unit 30 throughpump 33 for supplying motors 11A and 11B with the hydraulic fluid.

When fresh hydraulic fluid is filled into the hydraulic circuit of pump33 and motors 11A and 11B in the process of manufacturing vehicle 1,bypass valve 50 opens bypass duct 50 into communication with pumpchamber 30 b, as shown in FIG. 8, so as to pass hydraulic oil with wasteair from the fluid ducts formed in center section 30 d to pump chamber30 b, thereby properly filling hydraulic fluid without air bubbles inthe hydraulic circuit of pump 33 and motors 11A and 11B. The air in thefluid sump in pump chamber 30 b is finally exhausted to reservoir tank40 via pipe 87.

When vehicle 1 is hauled, bypass valve 50 also opens bypass duct 51 topump chamber 30 b so as to drain hydraulic fluid from the hydrauliccircuit, thereby allowing free rotation of drive wheels of vehicle 1.

Referring to FIG. 8, the higher and lower pressured hydraulic fluidducts and bypass duct 51, as shown in FIG. 3, are formed in centersection 30 d so as to communicate with hydraulic pump 33 mounted oncenter section 30 d. Bypass valve 50 comprises a horizontally axialvalve member 53 rotatably inserted into a horizontal valve chamber 52bored in center section 30 d across bypass duct 51 perpendicularly. Incenter section 30 d is also formed a drain passage 54 extended downwardfrom valve chamber 52. Drain passage 54 is downwardly open into pumpchamber 30 b through a gap between cylinder block 33 a (in detail, avalve plate between cylinder block 33 a and center section 30 d) of pump33 and the bottom surface of center section 30 d.

Valve member 53 is provided therein with an axial hole 55 a and apenetrating radial hole 55 b. Axial hole 55 a is constantly open at anouter end thereof to drain passage 54 through valve chamber 52 andconnected at an inner end thereof to radial hole 55 b. When valve member53 set in a closed-valve position for cutting off bypass duct 51 isviewed in sectional side, as shown in FIG. 8, holes 55 a and 55 b arearranged in a T-like shape so that hole 55 b is disposed inperpendicular to bypass duct 51. By rotational location of valve member53 to an open-valve position, open ends of radial hole 55 b are openedto bypass duct 51, i.e., radial hole 55 b makes complete bypass duct 51bypassing the higher and lower pressured hydraulic fluid ducts in centersection 30 d, whereby hydraulic fluid is drained from complete bypassduct 51 to pump chamber 30 b through hole 55 a, valve chamber 52 anddrain passage 54.

Valve member 53 projects at an outer end thereof outward from centersection 30 d and integrally rotatably fits to a rotary member 53 a,which is operatively connected to a manipulator (not shown) forswitching the rotational position of valve member 53 between theopen-valve position and the closed-valve position.

Front transaxle 10A will now be described in accordance with FIGS. 9 to13. In the following description, front transaxle 10A represents reartransaxle 10B because of their common main structures, thereby omittingdescription of rear transaxle 10B unless it is specially mentioned.

Referring to FIG. 9, transaxle 10A comprises a casing 61 whose internalspace is divided into a motor chamber 61 a, a brake chamber 61 b and adifferential gearing chamber 61 c. A hydraulic motor 11A (if intransaxle 10B, a hydraulic motor 11B) is disposed in motor chamber 61 a.A differential gearing assembly 71 is disposed in differential gearingchamber 61 c.

Deceleration gearing interposed between a motor shaft 11 a anddifferential gearing assembly 71 includes a first part provided on motorshaft 11 a and a second part provided on a counter shaft 62 c. In brakechamber 61 b are disposed a brake mechanism including a brake rotor 11 eon a motor shaft 11 a, and the first part of the deceleration gearingincluding a gear 11 d on motor shaft 11 a.

A vertical partition wall 61 s is formed in casing 61 so as to separatemotor chamber 61 a from brake chamber 61 b and differential gearingchamber 61 c. An intermediate gear 62, i.e., gears 62 a and 62 bprovided on counter shaft 62 c, serving as the second part of thedeceleration gearing, is disposed between chambers 61 b and 61 c incasing 61 so as to separate chambers 61 b and 61 c from each other.

Referring to FIGS. 10 and 11, casing 61 is dividable into a lower casingpart 61A and an upper casing part 61B along a horizontal joint surface.FIG. 9 illustrates only upper casing part 61B, i.e., casing 61 fromwhich lower casing part 61A is removed. Counter shaft 62 c and motorshaft 11 a have central axes disposed on the horizontal joint surfacebetween lower and upper casing parts 61A and 61B. Later-discussed axles19L and 19R are disposed higher than shafts 62 c and 11 a and supportedby upper casing part 61B.

Referring to FIG. 11, motor chamber 61 a and differential gearingchamber 61 c are mutually open through a passage 64 bored in partition61 s, thereby allowing flow of fluid between chambers 61 a and 61 c. Adiscoid magnet 65 is disposed in passage 64 so as to adsorb metallicimpurities such as iron powder in the fluid.

Referring to FIGS. 9 and 13, motor shaft 11 a, a cylinder block 11 b, amovable swash plate 11 c and a center section 12 are disposed in motorchamber 61 a so as to constitute variable displacement hydraulic motor11A.

Horizontal motor shaft 11 a is disposed laterally, i.e., perpendicularto the traveling direction of vehicle 1. Motor shaft 11 a is extended atone end thereof into brake chamber 61 b. The end portion of motor shaft11 a in brake chamber 61 b is toothed to serve as gear 11 d.

Referring to the brake mechanism in brake chamber 61 b as shown in FIG.9, discoid brake rotor 11 e is fixedly fitted on the end portion ofmotor shaft 11 a formed by extended gear 11 d. A pair of brake pads 11 fare disposed in brake chamber 61 b so as to pass brake rotor 11 etherebetween. A vertical camshaft 11 g is rotatably disposed adjacent topartition wall 61 s. An intermediate portion of camshaft 11 g issemicircular in sectional plan view so as to serve as a cam. One end ofcamshaft 11 g projects outward from casing 61 so as to be fixedlyprovided thereon with a brake arm 11 h, which is operatively connectedto a brake pedal or another braking operation device so as to beswitched between a braking position and a brake-releasing positionopposite to each other.

When brake arm 11 h is set to the brake-releasing position, the camportion of camshaft 11 g is fitted to partition wall 61 s so that thespace between brake pads 11 f is expanded so as to freely pass brakerotor 11 e therethrough. When brake arm 11 h is set at the brakingposition opposite to the brake-releasing position, the cam portion ofcamshaft 11 g faces to brake pads 11 f so as to press brake pads 11 fagainst brake rotor 11 e therebetween, thereby braking brake rotor 11 eand motor shaft 11 a.

Referring to FIG. 9, counter shaft 62 c between chambers 61 b and 61 cis disposed in parallel to motor shaft 11 a, and diametrically smallgear 62 b with diametrically large gear 62 a fixedly fitted thereon isfreely rotatably provided on counter shaft 62 c so as to serve asintermediate gear 62, i.e., the second part of the deceleration gearing.Large gear 62 a meshes with gear 11 d on motor shaft 11 a in brakechamber 61 b, and small gear 62 b meshes with a bull gear 72 ofdifferential gearing assembly 71 in differential gearing chamber 61 c.

Referring to FIGS. 9 to 12, differential gearing assembly 71 indifferential gearing chamber 61 c comprises bull gear 72, pinions 73,left and right axles 19L and 19R, and differential side gears 74L and74R fixed on respective axles 19L and 19R. In bull gear 72, pinionshafts 73 a are relatively rotatably disposed in a radial direction ofbull gear 72, and pinions 73 are fitted on respective pinion shafts 73a, as shown in FIG. 9. Horizontal axles 19L and 19R are disposedlaterally in parallel to motor shaft 11 a and counter shaft 62 c, andjournalled by upper casing part 11B. Proximal ends of axles 19L and 19Rare relatively rotatably fitted into vertical bull gear 72 so as toserve as the rotary axis of bull gear 72. Differential side gears 74Land 74R fixed on respective axles 19L and 19R mesh with each of pinions73 therebetween.

A differential locking mechanism for locking differential gearingassembly 71 is provided around left axle 19L, as shown in FIGS. 10 and12. Alternatively, such a mechanism may be provided around right axle19R. Referring to the differential locking mechanism shown in FIG. 12, avertical disk 75 is relatively rotatably supported on the proximal endof left axle 19L between bull gear 72 and side gear 74L. Fastener pins76 penetrate bull gear 72 and disk 75 together so as to fasten disk 75to bull gear 72. Namely, disk 75 is rotatable integrally with bull gear72 relative to left axle 19L.

Referring to FIGS. 9, 10 and 12, a guide sleeve 77 is relativelyrotatably fitted on axle 19L, and a ring-like slider 78 is axiallyslidably fitted on axle 19L. Slider 78 is provided with an annulargroove along the outer periphery thereof. A shifter 79 is fitted intothe annular groove so as to nip slider 78. An end of shifter 79 projectsoutward from casing 61 (lower casing part 61A) and engages with adifferential locking arm 79 a rotatably fitted onto lower casing part61A. Rotation of arm 79 a moves shifter 79 so as to slide slider 78along guide sleeve 77 in the axial direction of axle 19L. A spring 79 bis interposed between arm 79 a and lower casing part 61A so as to biasarm 79 a to its unlocking position for ensuring differential rotation ofaxles 19L and 19R.

Referring to FIGS. 9, 10 and 12, guide sleeve 77 is formed withsectionally semicircular grooves 77 a extended in parallel to axle 19Land juxtaposed with one another along the outer periphery of guidesleeve 77. Slider 78 is formed with sectionally semicircular grooves 78a extended in parallel to axle 19L and juxtaposed with one another alongthe inner periphery of slider 78. In the state that the outer peripheryof guide sleeve 77 coincides with the inner periphery of slider 78,grooves 78 a are arranged around axle 19L at regular intervalscorresponding to respective grooves 77 a so as to form sectionallycircular holes with grooves 77 a.

Referring to FIGS. 10 and 12, horizontal differential locking pins 81are inserted in the holes between guide sleeve 77 and slider 78. Morespecifically, each of pins 81 has an end portion 81 a fixedly insertedin each of the holes formed by grooves 78 a with grooves 77 a. The restportion of pin 81 diametrically larger than end portion 81 a is asliding portion slidably fitted to each of grooves 77 a of guide sleeve77. Differential side gear 74L is penetrated by holes 74 a arranged atregular intervals around axle 19L. Ends of sliding portions 81 b of pins81 opposite to end portions 81 a are slidably inserted into respectiveholes 74 a.

Holes 75 a corresponding to respective holes 74 a penetrate disk 75.When arm 79 a is disposed at the unlocking position, the ends of slidingportions 81 b of pins 81 are disposed in holes 74 a so as not to enterholes 75 a. When arm 79 a is disposed at the locking position, the endsof sliding portions 81 b of pins 81 project from holes 74 a and enterholes 75 a so as to fix slider 78 to disk 75, thereby locking axle 19Lto bull gear 72, i.e., canceling the differential rotation of axles 19Land 19R.

Incidentally, in FIG. 9, slider 78 looks as if it were divided by axle19L into a portion toward motor 11A and a portion opposite to motor 11Aaxially shifted from each other. Of course, such an appearance of slider78 is actually impossible. The illustration of slider 78 in FIG. 9 isjust for convenience of description of its actuation. The portion ofslider 78 with pin 81 separated from disk 75 on the side of axle 19Ltoward motor 11A is illustrated as being set when differential lockingarm 79 a is positioned at the unlocking position. The portion of slider78 with pin 81 inserted into disk 75 on the side of axle 19L opposite tomotor 11A is illustrated as being set when differential locking arm 79 ais positioned at the locking position.

Incidentally, disk 75 is made of material having such high strength asto prevent breaking thereof caused by the shock of insertion of slidingportions 81 b of pins 81 into penetrating holes 75 a of disk 75.Alternatively, disk 75 may be removed and pins 81 may be directlyinserted into bull gear 72. However, large bull gear 72 is made ofsintered metal having a small Charpy impact value for saving cost, andis penetrated by holes for supporting pinions 73. Such bull gear 72 maypossibly be broken by insertion of pins 81 thereinto. Therefore, highstrength disk 75 fastened to bull gear 72 is preferable.

Each of bypass valves 90 in respective transaxles 10A and 10B, as shownin FIGS. 10 and 13, is interposed on a bypass duct 12 f between higherand lower pressured hydraulic fluid ducts 12 c and 12 d connected toeach of hydraulic motors 11A and 11B. Bypass valve 90 normally cuts offbypass duct 12 f so as to ensure the proper circulation of hydraulicfluid between higher and lower pressured hydraulic fluid ducts 12 c and12 d in each of transaxles 10A and 10B for supplying motors 11A and 11Bwith the hydraulic fluid.

When fresh hydraulic fluid is filled into the hydraulic circuit of pump33 and motors 11A and 11B in the process of manufacturing vehicle 1,bypass valve 90 opens bypass duct 12 f into communication with motorchamber 61 a in casing 61, as shown in FIG. 13, so as to pass hydraulicoil with waste air from the hydraulic fluid ducts in center section 12to motor chamber 61 a, thereby properly filling hydraulic fluid withoutair bubbles in the hydraulic circuit of pump 33 and motors 11A and 11B.Air in each of transaxles 10A and 10B is finally exhausted to reservoirtank 40 through each of pipes 81 and 82.

When vehicle 1 is hauled, bypass valve 90 also opens bypass duct 12 f tomotor chamber 61 a so as to drain hydraulic fluid from the hydrauliccircuit, thereby allowing free rotation of drive wheels of vehicle 1.

Referring to FIGS. 10 and 13, a pair of kidney ports 12 a and 12 b arebored in center section 12 and open to hydraulic motor 11A (hereinafter,if in transaxle 10B, hydraulic motor 11B) mounted on center section 12.As shown in FIGS. 1, 9 and 10, horizontal pipe connectors 61 d and 61 eopened to respective kidney ports 12 a and 12 b are disposed on thehorizontal joint surface between upper and lower casing parts 61B and61A so as to be clamped by casings parts 61A and 61B. Pipe 84 isinterposed between pipe connector 61 e of rear transaxle 10B and pipeconnector 61 d of front transaxle 10A, pipe 83 is connected to pipeconnector 61 d of rear transaxle 10B, and pipe 85 to pipe connector 61 eof front transaxle 10A, as understood from FIGS. 2 and 3.

In center section 12, vertical holes 12 c and 12 d are extended upwardfrom respective kidney ports 12 a and 12 b, and a horizontal hole 12 fis bored between vertical holes 12 c and 12 d so as to form a bypassduct between kidney ports 12 a and 12 b. Bypass valve 90 comprises avertically axial valve member 92 rotatably inserted into a verticalvalve chamber 12 e bored in center section 12 across horizontal hole 12f of the bypass duct perpendicularly. In center section 12 is alsoformed a horizontal drain passage 12 g extended from valve chamber 12 e.Drain passage 12 g is open into motor chamber 61 a at a side surface ofcenter section 12 opposite to motor 11A.

In center section 12, valve member 92 is provided therein with an axialhole 95 a and a penetrating radial hole 95 b. Axial hole 95 a isconstantly open at an outer end thereof to drain passage 12 g throughvalve chamber 12 e and connected at an inner end thereof to radial hole95 b. When valve member 92 set in a closed-valve position for cuttingoff bypass duct 12 f is viewed in sectional front, as shown in FIG. 13,holes 95 a and 95 b are arranged in a T-like shape so that hole 95 b isdisposed in perpendicular to bypass duct 12 f. By rotational location ofvalve member 92 to an open-valve position, open ends of radial hole 95 bare opened to bypass duct 12 f, i.e., radial hole 95 b makes completebypass duct 12 f bypassing higher and lower pressured hydraulic fluidducts 12 c and 12 d in center section 12, whereby hydraulic fluid isdrained from complete bypass duct 12 f to motor chamber 61 a throughhole 95 a, valve chamber 12 e and drain passage 12 g.

Vertical valve member 92 penetrates an upright boss portion 61 g ofupper casing part 61B above center section 12 and projects upward fromupper casing part 61B so as to be fixed at the top thereof to ahorizontal lever 91, which is operatively connected to a manipulator(not shown) for switching the rotational position of valve member 92between the open-valve position and the closed-valve position.

A projection 91 a projects downward from arm 91, and two detent recesses61 f corresponding in location to projection 91 a are open upward on thetop surface of upper casing part 61B. Detent recesses 61 f contain aright angle therebetween centered on the central axis of valve member92, and are defined as the open-valve position and the closed-valveposition of bypass valve 90, respectively. In upper casing part 61Babove center section 12, a retaining ring 92 m is fixed on valve member92. The bottom of boss portion 61 g of upper casing part 61B is recessedupward so as to form a spring chamber 61 m, in which a spring 93 iswound around valve member 92 between retaining ring 92 m and a ceilingof spring chamber 61 m thereabove so as to press retaining ring 92 mdownward, thereby constantly biasing arm 91 downward and ensuring thedetent of projection 91 a into recess 61 f.

To shift bypass valve 90 between the open-valve position and theclosed-valve position, arm 91 is slightly raised against the downwardbiasing force of spring 93 so as to remove projection 91 a from one ofrecesses 61 f, and then, arm 91 is rotated to the other recess 61 f. Byreleasing arm 91, arm 91 is lowered by the spring force so as to fitprojection 91 a into the other recess 61 f.

Preferably, a clutch device 96 may be provided on motor shaft 11 a inbrake chamber 61 b, as shown in FIG. 14. In this embodiment, a motorgear 11 m is relatively rotatably provided on motor shaft 11 in brakechamber 61 b, and a laterally outer end of motor gear 11 m is radiallyextended to serve as a discoid brake rotor 11 n.

Clutch device 96 comprises a clutch slider 96 a not-relatively rotatablybut axially slidably spline-fitted on an end portion of motor shaft 11 aprojecting laterally outward from motor gear 11 m (brake rotor 11 n). InFIG. 14, clutch slider 96 a looks as if it were divided by motor shaft11 a into an upper portion and a lower portion axially shifted from eachother. Of course, such an appearance of clutch slider 96 is actuallyimpossible. The illustration of clutch slider 96 a in FIG. 14 is justfor convenience of description of its actuation. The upper portion ofclutch slider 96 a separated from brake rotor 11 n is illustrated asbeing set in an unclutching position. The lower portion of clutch slider96 a engaging with brake rotor 11 n is illustrated as being set in aclutching position.

A spring 11 s is coiled around motor shaft 11 a in clutch slider 96 a soas to bias clutch slider 96 a toward brake rotor 11 n (motor gear 11 m),thereby initially fixing clutch slider 96 a to brake rotor 11 n (motorgear 11 m), i.e., setting clutch slider 96 a to the clutching position.

An upright boss portion 61 h formed of upper casing member 61B aboveclutch slider 96 rotatably supports a vertical clutch operation shaft 97whose bottom projection 97 a is fitted into an annular groove formedalong the outer periphery of clutch slider 96 a. The vertical axis ofprojection 97 a is eccentric to the vertical axis of shaft 97. Clutchoperation shaft 97 projects upward from upper housing member 61B so asto be fixedly provided with a clutch arm 99.

Due to the eccentricity of projection 97 a relative to shaft 97, byrotating arm 99 together with shaft 97, shaft 97 is rotated by rotatingarm 99 so as to revolve projection 97 a around the axis of shaft 97,thereby moving clutch slider 96 along motor shaft 11 a. Arm 99 must beforcibly rotated against the biasing force of spring 11 s so as to shiftclutch slider 96 a to the unclutching position where clutch slider 96 ais separated from brake rotor 11 n.

When vehicle 1 is hauled, arm 99 is rotated for setting clutch slider 96a to the unclutcing position so as to make motor gear 11 m rotatablerelative to motor shaft 11 a, thereby drivingly separating intermediategear 62 and axles 19L and 19R from motor shaft 11 a, i.e., allowing freerotation of axles 19L and 19R. Even when motor gear 11 m is drivinglyseparated from motor shaft 11 a by the unclutching operation, thebraking operation for braking axles 19L and 19R is allowed due to brakerotor 11 n integrated with motor gear 11 m.

When hauling of vehicle 1, the above-mentioned bypass valve 90 may beoperated for draining so as to ensure free rotation of axles 19L and19R. The opening of bypass valves 90 of both transaxles 10A and 10Ballows rotation of both motors 11A and 11B free from pump 33. However,some remaining hydraulic fluid still circulates in the hydraulic circuitof pump 33 and motors 11A and 11B so that center section 12 resistscylinder block 11 b of each of motors 11A and 11B slidably rotatingthereon, thereby resisting rotation of axles 19L and 19R of each oftransaxles 10A and 10B. On the other hand, the unclutching of clutchdevice 96 of each of transaxles 10A and 10B perfectly drivinglyseparates axles 19L and 19R from each of motors 11A and 11B so thatvehicle 1 can be hauled by light traction force.

Incidentally, when clutch device 96 is not disposed in casing 61, bossportion 61 h of upper casing member 61B is plugged by a shaft 98replacing clutch operation shaft 97, as shown in FIG. 13, or such a bossportion 61 h for supporting shaft 97 is not formed in upper casingmember 61B.

Referring to a mechanism for adjusting the tilt of movable swash plate11 c, as shown in FIG. 9, swash plate 11 c has an engaged side 11 k towhich an engaging end 13 a of a control arm 13 disposed in casing 61 isfitted. Horizontal control shaft 14 is rotatably supported by casing 61(between upper and lower casing parts 61B and 61A), and an end ofcontrol arm 13 opposite to engaging end 13 a is fixed to an inner end ofshaft 14 in casing 61. As shown in FIG. 21, control lever 23 is fixedonto an outer end portion of shaft 14 outside casing 61. By rotatinglever 23 together with shaft 14, arm 13 is rotated so as to change thetilt angle of swash plate 11 c.

A mechanism for defining the tilt angle range of swash plate 11 ccomprises a shaft holder 15 for holding control shaft 14. A side wall ofcasing 61 is penetrated by a hole 61 v between motor chamber 61 a andthe outside of casing 61, as shown in FIG. 9. Shaft holder 15 includes aboss portion 15 a of shaft holder 15 having an axial penetrating hole 15b. Boss portion 15 a of shaft holder 15 is fitted into hole 61 v androtatably penetrated by control shaft 14 through hole 15 b. Shaft holder15 also includes a plate portion 15 c fitted onto an outer side surfaceof casing 61. Plate portion 15 c of shaft holder 15 is fastened by screwshafts with nuts (or bolts) 17 and 18 a to casing 61 so as to fix bossportion 15 a in location. As discussed later, by loosening the nuts orbolts, plate portion 15 c can be rotated around screw shaft 18 a so asto adjust the angle of boss portion 15 a relative to control shaft 14.

Shaft holder 15 can hold control shaft 14 and swash plate 11 c to berotatable so as to set corresponding motor 11A or 11B into the variabledisplacement type, and can determine the rotational limit of controlshaft 14 at the angle of swash plate 11 c defining the minimumdisplacement of corresponding motor 11A or 11B, whichever direction therotation of corresponding motor 11A or 11B may be set in relative to theflow direction of hydraulic fluid through motor 11A or 11B. In thisregard, referring to FIG. 15, boss portion 15 a is bored by a pair ofsubstantially radial eccentric holes 25 and 26 oppositely extended fromaxial penetrating hole 15 b. Control shaft 14 has a radial key slot 14 bwith a key 14 a fitted therein. Key 14 a projects radially outward froman end of slot 14 b so as to enter one of holes 25 and 26. While holes25 and 26 are so wide as to allow movement of key 14 a therein, therotational angle of key 14 a in each of holes 25 and 26 is limitedbetween angles A1 and A2, as shown in each of FIGS. 15 and 16.

When shaft 14 is located in rotation so as to set key 14 a to angle A1,swash plate 11 c is disposed so as to maximize the displacement ofcorresponding one of motors 11A and 11B. Control arm 13 has an upper endsurface 13 b and a lower end surface 13 c opposite to each other in therotational direction thereof. Control arm 13 is disposed between aninner horizontal surface 61 s of upper casing part 61B and an innerhorizontal surface 61 u of lower casing part 61A, which face to motorchamber 61 a therebetween. As shown in FIG. 15, when upper end surface13 b of control arm 13 abuts against inner horizontal surface 61 s ofupper casing part 61B downwardly facing to motor chamber 61 a, key 14 ais disposed at angle A1 so as to set swash plate 11 c for maximizing thedisplacement of corresponding motor 11A or 11B. When shaft 14 is locatedin rotation so as to set key 14 a to angle A2, swash plate 11 c isdisposed so as to minimize the displacement of corresponding one ofmotors 11A and 11B.

Hole 25 has end surfaces opposite to each other in the rotationaldirection of key 14 a (shaft 14), and one of the end surfaces is an endsurface 25 a for limiting movement of key 14 a in hole 25. Hole 26 alsohas a similar end surface 26 a for limiting movement of key 14 a in hole26. In the embodiment of FIG. 15, when key 14 a abuts against endsurface 25 a of hole 25, key 14 a is disposed at angle A2 so as to setswash plate 11 c for minimizing the displacement of corresponding motor11A or 11B.

By changing the angle of boss portion 15 a relative to control shaft 14,shaft holder 15 can adjust angle A2 of key 14 a of control shaft 14 soas to adjust the minimum displacement of corresponding motor 11A or 11B.In this regard, as shown in FIG. 15( a), a first slot 15 d is bored inplate portion 15 c of shaft holder 15. An eccentric bush 18 b is passedthrough first slot 15 d. Eccentric bush 18 b has an eccentrically axialpenetrating hole 18 c through which screw shaft 18 a is passed andscrewed into casing 61 (lower casing part 61A). Screw shaft 18 a isprovided thereon with a nut, or formed at an outer end thereof into abolt head, so as to be fastened to casing 61 together with eccentricbush 18 b. By loosening shaft 18 a from casing 61, eccentric bush 18 bcan be revolved around shaft 18 a so as to revolve plate portion 15 caround the axis of boss portion 15 a and shaft 14, thereby changing theangle of boss portion 15 a relative to control shaft 14, i.e., adjustingangle A2 of key 14 a defining the minimum displacement of correspondingmotor 11A or 11B.

Plate portion 15 c of shaft holder 15 is also bored by a second slot 15e, through which screw shaft 17 (provided with a nut, or formed into abolt) is passed and screwed into casing 61 (lower casing part 61A) so asto fasten plate portion 15 c of shaft holder 15 adjusted in angle tocasing 61. During the above adjusting of angle A2 of key 14 a, screwshaft 17 fixed to casing 61 relatively moves along second slot 15 e soas to allow and guide the rotation of plate portion 15 c.

The minimum displacement of each of motors 11A and 11B defines themaximum rotary speed of axles 19L and 19R on the assumption that thedisplacement of pump 33 and the rotary speed of pump shaft 30 p areconstant. Due to the above construction, the minimum displacement ofmotor 11A or 11B can be adjusted so as to adjust the maximum rotaryspeed of axles 19L and 19R to an optimal value for preventing drivewheels provided on axles 19L and 19R from dragging on a turf, or forensuring an optimal difference of rotary speed between front and reardrive wheels for turning of vehicle 1.

The rotational direction of control shaft 14 and swash plate 11 c forreducing the displacement of corresponding motor 11A or 11B may be setopposite to that of FIG. 15, in correspondence to such a situation thatthe relation of rotational direction of axles 19L and 19R to the flowdirection of hydraulic fluid through corresponding motor 11A or 11B isreversed, i.e., that the flow direction of hydraulic fluid through motor11A or 11B is opposite to that of FIG. 15 while the rotational directionof axles 19L and 19R is the same as that of FIG. 15. In this state,shaft holder 15 is arranged so as to insert key 14 a of control shaft 14into hole 26 opposite to hole 25 with respect to the axis of shaft 14,as shown in FIG. 16.

In the arrangement of shaft holder 15 as shown in FIG. 16, when key 14 aabuts against end surface 26 a of hole 26, key 14 a is disposed at angleA2 so as to set swash plate 11 c for minimizing the displacement ofcorresponding motor 11A or 11B. Furthermore, when lower end surface 13 cof control arm 13 abuts against inner horizontal surface 61 u of lowercasing part 61A upwardly facing to motor chamber 61 a, key 14 a isdisposed at angle A1 so as to set swash plate 11 c for maximizing thedisplacement of corresponding motor 11A or 11B.

Referring to FIG. 17, shaft holder 15 can also hold a control shaft 14′replacing control shaft 14 to be immovable so as to fix swash plate 11c, i.e., set corresponding motor 11A or 11B into the fixed displacementtype. Control shaft 14′ has a diametrical key groove 14′b in which adiametrically penetrating key 14′a is fitted. In this regard, as shownin FIGS. 15 to 17, a pair of opposite radial holes 27 for fitting key14′a therein are bored in boss portion 15 a of shaft holder 15, andextended from axial penetrating hole 15 b substantially perpendicularlyto holes 25 and 26. Holes 27 are so narrow as to tighten key 14′ainserted therein, thereby preventing control shaft 14′ from rotating.Key 14′a of control shaft 14′ is so arranged as to be tightly fittedinto both holes 27, as shown in FIG. 17.

Even in this state, by loosening shaft 17 and revolving eccentric sleeve18 b around rotary axial shaft 18 a, boss portion 15 a can be rotated soas to adjust the fixed angle of swash plate 11 c.

To sum up, each of transaxles 10A and 10B incorporates correspondingvariable displacement hydraulic motor 11A or 11B provided with means fordetermining a tilt angle range of a movable swash plate thereof, whereinthe means can also change the movable swash plate into a fixed swashplate, that is, change the variable displacement hydraulic motor into afixed displacement hydraulic motor. Namely, each of transaxles 10A and10B uses the common means for adjusting the displacement ofcorresponding motor 11A or 11B whether the displacement is set variableor constant, thereby being applicable to various type vehicles.

In a vehicle having a turning center shifted lengthwise from the middlepoint between its front wheels and rear wheels, front and reartransaxles 10A and 10B are preferably provided with respective hydraulicmotors 11A and 11B one of which is a variable displacement type, and theother of which is a fixed displacement type, so that the variable motordisplacement defining its rotary speed can be changed to preventdragging of grounding wheels during turning of the vehicle.

For example, in working vehicle 1 as show in FIG. 1, preferably,hydraulic motor 11A of front transaxle 10A for driving steerable wheelsis set into a variable displacement type, and hydraulic motor 11B ofrear transaxle 10B for driving unsteerable wheels is set into a fixeddisplacement type. During turning of vehicle 1, the turning center ofvehicle 1 is disposed on the cross point between the axial extensionline of axles 19L and 19R of rear transaxle 10B and that of axles 19Land 19R of front transaxle 10A so that the steerable wheels supported byfront transaxle 10A are further distant from the turning center than theunsteerable wheels supported by rear transaxle 10B. Considering thissituation, preferably, hydraulic motor 11A of transaxle 10A is set so asto reduce its displacement, i.e., increase its output rotary speed,according to turning of the vehicle, thereby preventing dragging of thesteerable wheels. In this case, transaxle 10A has shaft holder 15rotatably holding control shaft 14, whose key 14 a in hole 25 or 26 isnormally disposed at angle A1 when the vehicle travels straight, andturned to angle A2 during turning of the vehicle. Transaxle 10B hasshaft holder 15 holding control shaft 14, whose key 14 a is tightened inholes 27.

An articulated working vehicle 200 as shown in FIGS. 22 and 23 comprisesa rear frame 203 and a front frame 204 mutually flexibly connected via acoupling 205. Transaxle 10A is mounted on front frame 204, and transaxle10B on rear frame 203. Coupling 205 (more specifically, a line B1passing the vertical axial center of coupling 205) is shifted forwardfrom a middle line B2 between the axial center line of axles 19L and 19Rof transaxle 10A and the axial center line of axles 19L and 19R oftransaxle 10B, i.e., coupling 205 is eccentrically disposed toward theaxial center line of axles 19L and 19R of transaxle 10A. Therefore, asthe turning angle of vehicle 200 increases, tires supported by fronttransaxle 10A are further distant from the turning center of vehicle 200than tires supported by rear transaxle 10B. Correspondingly, it isrequested that either or both of hydraulic motors 11A and 11B ofrespective transaxles 10A and 10B are set into the variable displacementtype so that the tires of transaxle 10A can increase their rotary speedfaster than the tires of rear transaxle 10B according to increase of theturning angle of vehicle 200. For example, hydraulic motor 11A oftransaxle 10A on front frame 204 is set into the variable displacementtype, and hydraulic motor 11B of transaxle 10B on rear frame 203 is setinto the fixed displacement type. During turning of vehicle 200,hydraulic motor 11A is reduced in displacement for increasing its outputrotary speed according to increase of the turning angle of vehicle 200,thereby preventing dragging of tires.

Alternatively, if coupling 205 of articulated vehicle 200 is shiftedbackward (toward the axial center line of axles 19L and 19R of reartransaxle 10B) from middle line B2, hydraulic motor 11A of fronttransaxle 10A is set in the variable displacement type, and hydraulicmotor 11B of rear transaxle 10B is set in the fixed displacement type.In this case, it is considerable that hydraulic motor 11A of fronttransaxle 10A is increased in displacement for reducing its outputrotary speed. Alternatively, if articulated vehicle 200 has coupling 205on middle line B2, i.e., such that no difference of rotary speed betweenthe front tires and the rear tires is required during turning, it may beconsidered that both hydraulic motors 11A and 11B of respectivetransaxles 10A and 10B are set in the fixed displacement type.

A mechanism of supporting transaxle 10A at a front portion of chassis 3of vehicle 1 will be described in accordance with FIGS. 18 to 21.Incidentally, as discussed later, FIGS. 18 to 21 show guide plate 151guiding control lever 23 instead of shaft holder 15 holding controlshaft 14.

Referring to FIGS. 18 and 19, a front bracket plate 3 a and a rearbracket plate 3 b are hung down from chassis 3 so as to pivotallysupport a center pin 3 c extended in the longitudinal direction ofvehicle 1. A support frame 110 is pivoted at an upper portion thereof oncenter pin 3 c between bracket plates 3 a and 3 b. As shown in FIG. 20,support frame 110 includes a pair of vertical front and rear plates 111and 112, each of which is bent into a substantially trapezoidal shapewhen viewed in plan. A horizontal sleeve 113 relatively rotatablypenetrated by center pin 3 c is extended in the longitudinal directionof vehicle 1 so as to connect plates 111 and 112 to each other. A pairof left and right substantially horizontal plates 114 and 115 areextended in the longitudinal direction of vehicle 1 so as to connectplates 111 and 112 to each other. A substantially horizontal upper plate116 bent into different levels is extended along upper edges of plates111 and 112 so as to cover the space between plates 111 and 112therebelow, as best shown in FIG. 19.

As shown in FIGS. 18 to 20, upper casing part 61B of casing 61 oftransaxle 10A is formed with left and right axle housing portions forsupporting respective axles 19L and 19R, which are fitted at topsurfaces thereof to lower surfaces of plates 114 and 115, and fastenedto plates 114 and 115 by bolts 117, respectively.

As shown in FIGS. 19 to 21, front and rear plates 111 and 112 are boredby holes 118 through which pipes 84 and 85 can be passed.

As shown in FIG. 19, left and right tires 140L and 140R are laterallyrotatably supported onto left and right ends of support frame 110,respectively. Each of tires 140L and 140R is provided with a pair ofupper and lower substantially vertical and coaxial king pins 143 a and143 b. Upper king pins 143 a are supported by respective left and rightends of upper plate 116 projecting laterally outward from left and rightends of plates 111 and 112. Left and right substantially horizontalplates 141L and 141R are extended between left and right lower edges ofplates 111 and 112, and project laterally outward from the left andright ends of plate 111 and 112 so as to support respective lower kingpins 143 b.

A bearing casing 144 fixedly penetrates a vertical plate portion of abracket 148, which is bent to have upper and lower substantiallyhorizontal plate portions. The upper and lower substantially horizontalplate portions of each bracket 148 are extended laterally inward, sothat the upper plate portion is pivotally connected to upper plate 116via upper king pin 143 a, and the lower plate portion to each of plates141L and 141R via lower king pin 143 b.

Each of tires 140L and 140R is provided on the periphery of a wheel (orrim) 146, to which an axial center shaft 145 is fixed. Axial centershafts 145 of tires 140L and 140R rotatably penetrate bearing casings144 to be pivotally connected to axles 19L and 19R via universal joints124L and 124R disposed between upper and lower king pins 143 a and 143b, respectively. In this way, left and right tires 140L and 140R arelaterally rotatably and drivingly connected to respective axles 19L and19R of transaxle 10A.

As shown in FIGS. 19 and 20, the substantially horizontal lower plateportion of right bracket 148 provided to right tire 140R is extendedlaterally inward from king pin 143 b so as to serve as a stay 149pivotally connected to one end of a link rod 123 operatively connectedto steering wheel 7. As shown in FIG. 20, tires 140L and 140R areprovided with respective arms 121L and 121R horizontally rotatablypivoted on either king pins 143 a or 143 b. A tie rod 122 is pivotallyinterposed between arms 121L and 121R. Due to this construction, bothtires 141L and 141R are laterally turned by rotating steering wheel 7.

As shown in FIGS. 20 to 21, right bracket 148 has a forward projection148 a operatively connected to control shaft 14 serving as the rotaryaxis of swash plate 11 c of motor 11A in transaxle 10A. Therefore, thedisplacement of motor 11A is changed according to detection of lateralturning of tires 140L and 140R.

As shown in FIG. 21, control lever 23 is fixed on horizontal controlshaft 14 pivotally supported by casing 61 of transaxle 10A, so as to bevertically rotatable together with control shaft 14. A lever guidemechanism 150 is provided for guiding rotation of lever 23 according tomovement of link rods 126 and 127 extended from forward projection 148 aof bracket 148.

Lever guide mechanism 150 comprises a vertical cam plate 151 pivoted tocasing 61 (upper casing part 61B) via a horizontal pivot shaft 152. Asshown in FIG. 21, cam plate 151 is fan-shaped when viewed in front,formed with a substantially arcuate guide slot 151 a along its arcuateedge. In guide slot 151 a, a center portion thereof is most distant frompivot shaft 152. As going to each of upper and lower ends of slot 151 afrom the center portion, the distance between slot 151 a and pivot shaft152 decreases.

Cam plate 151 has a joint point 151 b adjacent to the upper end of guideslot 151 a so as to join with an end of link rod 127.

A horizontal collar 23 a is relatively rotatably provided on a tip ofcontrol lever 23 and slidably rotatably fitted into guide slot 151 a.When vehicle 1 travels straight (tires 140L and 140R are oriented in theforward and backward direction of vehicle 1), collar 23 a is disposed atthe center portion of guide slot 151 a evenly distant from both theupper and lower ends thereof.

Whether vehicle 1 turns left or right, link rods 126 and 127 interposedbetween bracket 148 of right tire 140R and cam plate 151 is pushed orpulled so as to rotate cam plate 151 around pivot shaft 152, wherebycollar 23 a approaches either the upper or lower end of guide slot 151a. Collar 23 a approaching either the upper and lower end of guide slot151 a approaches pivot shaft 152 because of the above-mentionedreduction of distance between guide slot 151 a and pivot shaft 152,thereby rotating the tip of control lever 23 toward pivot shaft 152. Ifthis rotational direction of lever 23 corresponds to the rotationaldirection of swash plate 11 c for reduction of the displacement of motor11A, tires 140L and 140R of transaxle 10A are accelerated according toincrease of their left or right turning angle.

As shown in FIG. 21, an expansion joint 125 is interposed between linkrod 126 joined to front projection 148 a of bracket 148 and link rod 127joined to cam plate 151. Expansion joint 125 is provided for allowingthe turning of tires 140L and 140R after control lever 23, i.e., swashplate 11 c reaches its rotational limit position if the turning range oftires 140L and 140R exceeds that of control lever 23. Expansion joint125 comprises a casing 125 a incorporating a spring 125 b. Link rod 126extended from projection 148 a is screwed into one end of casing 125 a,and link rod 127 extended from cam plate 151 is axially slidablyinserted into casing 125 a through the other end of casing 125 a.

In casing 125 a, spring 125 b is disposed between slide retainers 127 aand 127 b axially slidably provided on link rod 127. Slide retainer 127a is nearer to link rod 126 than slide retainer 127 b. A stopper pin 127e is radially inserted into an end portion of link rod 127 so as toprevent slide retainer 127 a from excessively moving on link rod 127toward link rod 126. A washer 127 d is provided on link rod 127 betweenstopper pin 127 e and slide retainer 127 a. A retaining ring 125 c isfixedly provided on the inner periphery of casing 125 a so as to preventslide retainer 127 a from excessively moving toward link rod 126, i.e.,limit the movement of casing 125 a relative to link rod 127 toward camplate 151.

In casing 125 a, link rod 127 has a diametric difference, and a washer127 c is disposed on link rod 127 between the diametric difference andslide retainer 127 b. The diametric difference of link rod 127 preventsslide retainer 127 b with washer 127 c from excessively moving on linkrod 127 away from link rod 126. The end surface of casing 125 a passinglink rod 127 therethrough prevents flange retainer 127 b fromexcessively moving away from link rod 126, i.e., limits the movement ofcasing 125 a relative to link rod 127 away from cam plate 151.

If the whole left and right turning range of tires 140L and 140R isensured during the whole rotation of swash plate 11 c, spring 125 b maybe unused. However, it may happen that the rotatable range of swashplate 11 c is unexpectedly reduced by dimensional error so that swashplate 11 c reaches its limit angle before the turning of tires 140L and140R reaches the limit. When control lever 23 is stopped by swash plate11 c reaching the limit angle, link rod 127 and cam plate 151 stop.However, tires 140L and 140R can still turn while control lever 23stops, because casing 125 a connected to bracket 148 via link rod 126allows relative axial movement of link rod 127 therein.

If tires 140L and 140R are going to turn left after stopping of controllever 23, casing 125 a slides toward cam plate 151 relative to link rod127 so as to allow the further left turning of tires 140L and 140R.Casing 125 a sliding toward cam plate 151 along link rod 127 pushesslide retainer 127 a toward slide retainer 127 b retained by thediametric difference of link rod 127, thereby compressing spring 125 bso as to resist the left turning of tires 140L and 140R while controllever 23 and swash plate 11 c are stopped.

If tires 140L and 140R are going to turn right after stopping of controllever 23, casing 125 a slides away from cam plate 151 relative to linkrod 127 so as to allow the further right turning of tires 140L and 140R.Casing 125 a sliding away from cam plate 151 along link rod 127 pushesslide retainer 127 b toward slide retainer 127 a retained by retainingring 125 c, thereby compressing spring 125 b so as to resist the rightturning of tires 140L and 140R while control lever 23 and swash plate 11c are stopped.

Articulated working vehicle 200 as shown in FIGS. 22 and 23 comprisesrear frame 203 and front frame 204 flexibly coupled to each otherthrough coupling 205. Rear frame 203 supports engine 4, pump unit 30,reservoir tank 40 and transaxle 10B, and front frame 204 supportstransaxle 10A. Similar to vehicle 1, the hydraulic circuit forcirculating hydraulic fluid among hydraulic pump 33 and motors 11A and11B is constructed by piping of pipes 81, 82 and so on among pump unit30, transaxles 10A and 10B and reservoir tank 40 (the piping is omittedin FIG. 22).

Each of front and rear transaxles 10A and 10B is laterally eccentricallydisposed in vehicle 1 so that left and right axles 19L and 19Rprojecting laterally outward therefrom are different in length from eachother. Left and right brackets 203 a and 204 a holding respectivebearings are hung down from rear frame 203 and front frame 204 so as tojournal respective axles 19L and 19R through the respective bearingsadjacent to front and rear tires on outer ends of axles 19L and 19R.

In FIGS. 22 and 23, pump unit 30 incorporating hydraulic pump 33 havingvertical pump shaft 30 p and a reservoir tank 40 are laterallyjuxtaposed on rear frame 203 and disposed between front and reartransaxles 10A and 10B. However, any place in vehicle 200 and anydirection are allowed for arranging pump unit 30 if pump unit 30 can bedrivingly connected to engine 4 properly, similarly to vehicle 1. Forexample, pump unit 30 may alternatively be disposed before fronttransaxle 10A or behind rear transaxle 10B. Alternatively, pump unit 30may be disposed over or below the longer one of axles 19L and 19R ofeither rear transaxle 10B or front transaxle 10A so that pump unit 30and either rear transaxle 10B or front transaxle 10A are laterallyjuxtaposed between left and right brackets 203 a or 204 a.Alternatively, pump unit 30 may be disposed to orient pump shaft 30 phorizontally. Further, other place and height than the illustrated maybe allowed for arranging reservoir tank 40 because of the same reason inthe description of vehicle 1.

In coupling 205, a vertical pivot shaft 206 is rotatably supported byframes 203 and 204. A pair of upper and lower pulleys 207 and 208 arefixed on a lower portion of pivot shaft 206. A belt 211 is interposedbetween pulley 207 and a pulley 209 fixed on the vertical output shaftof engine 4, and a belt 212 is interposed between pulley 208 and apulley 213 fixed on a vertical input shaft of mower 210, therebytransmitting engine power to mower 210.

Referring to FIG. 23, considering that articulation of vehicle 200 viacoupling 205 changes distances among pump unit 30 and transaxles 10A and10B, pipes 81, 84 and 85 for connecting pump unit 30 and transaxles 10Aand 10B to one another are made of elastic material, such as rubber.Alternatively, each of pipes 81, 84 and 85 may be combination of arubber pipe and a metal pipe facilitating effective radiation.

Referring to FIG. 23, as mentioned above, line B1 passing the axialcenter of coupling 205 is shifted forward from the above-mentionedmiddle line B2 of vehicle 200 so that, as vehicle 200 turns, thedistance of drive wheels of transaxle 10A from a turning center ofvehicle 200 becomes larger than that of transaxle 10B. Therefore, asmentioned above, during turning of vehicle 200, the displacement ofmotor 11A in transaxle 10A is reduced so as to increase the wheel speedof the drive wheels (tires 140L and 140R) of transaxle 10A to a valuelarger than that of the drive wheels of transaxle 10B, therebypreventing dragging of the drive wheels of transaxle 10A. The same istrue about vehicle 1. That is, each of vehicle 1 having the steerablefront wheels and the unsteerable rear wheels and articulate vehicle 200having the forwardly shifted articulation pivot requires acceleration ofthe front wheels driven by front transaxle 10A during turning of thevehicle.

Referring to FIG. 24, two patterns S1 and S2 about setting front andrear transaxles 10A and 10B are provided for vehicles 1 and 200considering such a necessity of accelerating the drive wheels of fronttransaxle 10A during turning of the vehicle. Whether transaxles 10A and10B may be set in pattern S1 or S2, a wheel speed D1 or D2 of the drivewheels of transaxle 10A is equal to a wheel speed D3 of the drive wheelsof transaxle 10B during straight traveling of the vehicle, and wheelspeed D1 or D2 of the drive wheels of transaxle 10A becomes larger thanwheel speed D3 of the drive wheels of transaxle 10B during turning ofthe vehicle.

Conventional setting pattern S1 is established when front and reartransaxles 10A and 10B are essentially standardized excluding that fronthydraulic motor 11A is variable in displacement and hydraulic motor 11Bis fixed in displacement. The deceleration gearing interposed betweenmotor shaft 11 a and axles 19L and 19R in front transaxle 10A is thesame with that in rear transaxle 10B so that a gear reduction ratio G1of transaxle 10A for changing a motor shaft speed R1 into wheel speed D1is equal to a gear reduction ratio G3 of transaxle 10B for changing amotor shaft speed R3 into wheel speed D3.

In the arrangement in each of transaxles 10A and 10B, as shown in FIG.9, motor gear 11 d on motor shaft 11 a, intermediate gear 62, bull gear72, pinions 73 and differential side gears 74L and 74R are determined innumber of teeth thereof so as to determine each of gear reduction ratiosG1 and G3. In other words, increase of gear reduction ratio meansincrease of gear teeth of the deceleration gearing.

Corresponding to the equality of gear reduction ratios G1 and G3, motorshaft speed R1 of transaxle 10A (the rotary speed of motor shaft 11 a ofhydraulic motor 11A) must be equal to motor shaft speed R3 (the rotaryspeed of motor shaft 11 a of hydraulic motor 11B) of transaxle 10Bduring straight traveling of the vehicle. It means that a motordisplacement R1 of transaxle 10A (the variable displacement of hydraulicmotor 11A) must be equal to a motor displacement R3 of transaxle 10B(the fixed displacement of hydraulic motor 11B) during straighttraveling of the vehicle.

A problem of conventional setting pattern S1 arises during turning ofthe vehicle. As mentioned above, wheel speed D1 of transaxle 10A must beincreased to a value larger than wheel speed D3 of transaxle 10B duringturning of the vehicle, so that movable swash plate 11 c of hydraulicmotor 11A must be moved to reduce variable motor displacement M1 oftransaxle 10A to a value smaller than constant motor displacement M3 oftransaxle 10B so as to increase motor shaft speed R1 of transaxle 10A toa value larger than constant motor shaft speed R3 of transaxle 10B.Increase of motor shaft speed M1 means acceleration of the decelerationgearing of transaxle 10A. However, the deceleration gearing isstandardized in its gear teeth count or the like so as to correspond totransaxle 10B having fixed displacement hydraulic motor 11B. In otherwords, the deceleration gearing is not standardized in anticipation ofincrease of the motor shaft speed. If such a deceleration gearing isaccelerated by increase of the motor shaft speed, unexpectedly largenoise is possibly generated.

Setting pattern S2 is presented for solving the problem of conventionalsetting pattern S1. In setting pattern S2, transaxle 10A has a motordisplacement M2 larger than fixed motor displacement M3 of transaxle 10Bduring straight traveling of the vehicle, so that motor shaft speed R2of transaxle 10A is smaller than motor shaft speed R3 of transaxle 10Bduring straight traveling of the vehicle. Correspondingly, transaxle 10Ais provided with a deceleration gearing having gear reduction ratio G2smaller than gear reduction ratio G3 of the deceleration gearing oftransaxle 10B so as to equalize its wheel speed D2 to wheel speed D3 oftransaxle 10B during straight traveling of the vehicle.

During turning of the vehicle, transaxle 10A reduces its motordisplacement M2 so as to increase its motor shaft speed R2, therebyincreasing its wheel speed D2 to a value larger than wheel speed D3 oftransaxle 10B. Even if reduced motor displacement M2 reaches a value notmore than fixed motor displacement M3 of transaxle 10B so that motorshaft speed R2 reaches a value not less than motor shaft speed R3 oftransaxle 10B, noise generated from the deceleration gearing oftransaxle 10A accelerated by the increase of motor shaft speed R2 isstill suppressed to an acceptable value because of its small gearreduction ratio G2 (smaller than gear reduction ratio G3 of transaxle10B). Consequently, vehicle 1 or 200 having transaxles 10A and 10B setin pattern S2 can turn under the suppressed noise condition.

Incidentally, to make motor displacement M2 larger than motordisplacement M3 during straight traveling of the vehicle, transaxle 10Amay have hydraulic motor 11A having its internal displacement (definedby its essential cylinder volume or so on) larger than the internaldisplacement of hydraulic motor 11B of transaxle 11B, or hydraulicmotors 11A and 11B may have equal internal displacements, while movableswash plate 11 c of hydraulic motor 11A is set to increase motordisplacement M2 to the required level.

FIG. 25 illustrates alternative pump unit 30 disposed below chassis 3 ofvehicle 3 or rear frame 203 of vehicle 200. A bracket 3 b or 203 b hungdown from chassis 3 or rear frame 203 is a plate bent in a U-like shapewhen viewed in side. That is, bracket 3 b (203 b) has vertical front andrear portions and a lower horizontal portion between the vertical frontand rear portions. Pump unit 30 is hung down from the horizontal portionof bracket 3 b (203 b). Pump unit 30 is vertically reversed incomparison with that of FIG. 1 (FIG. 22) so that charge pump 32 isdisposed below hydraulic pump 33.

Pump shaft 30 p projects upward from the horizontal portion of bracket 3b (203 b). The portion of pump shaft 30 p between chassis 3 (203) andthe horizontal portion of bracket 3 b (203 b) below chassis 3 (rearframe 203) is fixedly provided thereon with cooling fan 34 b and inputpulley 35. Vertical output shaft 4 a of engine 4 projects downward fromchassis 3 (rear frame 203) adjacent to bracket 4 b (203 b) so as to befixedly provided thereon with output pulley 4 b which is tied with inputpulley 35 by belt 4 c. Cooling fan 34 b blows cooling wind downwardtoward pump unit 30 therebelow, rear transaxle 10B adjacent to pump unit30, and pipes disposed therearaound. Bracket 3 b (203 b) is open at bothleft and right sides thereof so as to expose cooling fan 34 b to theopen air, thereby supplying air to cooling fan 34 b.

Although the invention has been described in its preferred from which acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been changed in the details ofconstruction and the combination and arrangement of parts may beresorted to without departing from the spirit and the scope of theinvention as hereinafter claimed.

1. A hydraulic driving vehicle comprising: a front transaxle and a rear transaxle, each incorporating a hydraulic motor; a pump unit separated from the front and rear transaxles, the pump unit incorporating a hydraulic pump having a pump shaft; a hydraulic circuit formed by piping among the pump unit and the front and rear transaxles so as to circulate hydraulic fluid among the hydraulic pump and the hydraulic motors; a reservoir tank of the hydraulic fluid connected to the hydraulic circuit by piping; and a first cooling fan drivingly connected to the pump shaft, the first cooling fan blowing air away from the pump unit, wherein at least one pipe for the piping of the hydraulic circuit and the reservoir tank passes an area blown by the first cooling fan.
 2. The hydraulic driving vehicle as set forth in claim 1, wherein one of the front and rear transaxles is disposed so as to pass the area blown by the first cooling fan.
 3. The hydraulic driving vehicle as set forth in claim 1, wherein the front and rear transaxles and the pump unit are connected through respective separate pipes to the reservoir tank so as to drain excessive fluid to the reservoir tank individually.
 4. The hydraulic driving vehicle as set forth in claim 1, wherein at least one pipe for the piping of the hydraulic circuit and the reservoir tank is partly or entirely made of metal material.
 5. The hydraulic driving vehicle as set forth in claim 1, further comprising: a hydraulic actuator driven by the hydraulic pump, wherein a pipe for piping the hydraulic actuator to the hydraulic circuit passes the area blown by the first cooling fan.
 6. The hydraulic driving vehicle as set forth in claim 1, further comprising: a second cooling fan drivingly connected to the pump shaft and disposed opposite to the first cooling fan with respect to the hydraulic pump, the second cooling fan blowing air toward the pump unit, wherein at least one pipe for the piping of the hydraulic circuit and the reservoir tank passes an area blown by the second cooling fan.
 7. The hydraulic driving vehicle as set forth in claim 6, wherein the front and rear transaxles and the pump unit are connected through respective separate pipes to the reservoir tank so as to drain excessive fluid to the reservoir tank individually.
 8. The hydraulic driving vehicle as ser forth in claim 6, wherein at least one pipe for the piping of the hydraulic circuit and the reservoir tank is partly or entirely made of metal material.
 9. The hydraulic driving vehicle as set forth in claim 6, further comprising: a hydraulic actuator driven by the hydraulic pump, wherein a pipe for piping the hydraulic actuator to the hydraulic circuit passes the area blown by the first or second cooling fan.
 10. A hydraulic driving vehicle comprising: a front transaxle and a rear transaxle, each incorporating a hydraulic motor; a pump unit separated from the front and rear transaxles, the pump unit incorporating a hydraulic pump; a hydraulic circuit formed by piping between the pump unit and the front and rear transaxles so as to circulate hydraulic fluid among the hydraulic pump and the hydraulic motors; and a reservoir tank of the hydraulic fluid connected to the hydraulic circuit by piping, wherein the reservoir tank includes a plurality of separate ports connected to the respective front and rear transaxles and pump unit through respective separate pipes to the reservoir tank so as to drain excessive fluid to the so as to receive fluid drained from the respective front and rear transaxles and pump unit.
 11. The hydraulic driving vehicle as ser forth in claim 10, wherein at least one pipe for the piping of the hydraulic circuit and the reservoir tank is partly or entirely made of metal material. 